Set up the bones of a Flask app with configuration

src/config/parse.py

@@ -0,0 +1,20 @@
+from typing import Any
+
+
+class ConfigParseError(Exception):
+    """An error for when parsing a config fails"""
+
+    def __init__(self, keypath: list[str], issue: str):
+        path = '.'.join(keypath)
+        message = f'{path}: {issue}'
+        super().__init__(message)
+        self.keypath = keypath
+        self.issue = issue
+
+
+def assert_key_of_type(config: dict[str, Any], key: str, kind: Any):
+    if key not in config:
+        raise ConfigParseError([key], 'missing')
+
+    if not isinstance(config[key], kind):
+        raise ConfigParseError([key], f'type of "{key}" was {type(config[key])}, expected {kind}')